Intra-frame code diversity

ABSTRACT

Provided are methods and apparatuses to encode portions of user data with corresponding spreading sequences within a frame wherein the user data is associated with a single user.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. provisionalapplication Ser. No. 60/601,287, filed Aug. 12, 2004, the disclosure ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to mobile radio signal diversity, and moreparticularly, to encoding downlink and uplink mobile radio datatransmitted in multiple timeslots within a frame from a single source,wherein portions of the data are encoded with different spreadingsequences.

2. Description of the Prior Art

Data is transmitted in CDMA radio systems by means of sending a codesequence for each bit or data symbol. Each user is assigned a differentcode. If a user transmits data on multiple channels, each user channelis assigned a different code. By using different codes, multiple usersmay transmit signals within the same frequency band within the sametimeslot. The codes are generally designed such that they have goodcross-correlation properties. Good cross-correlation properties allow areceiver to correlate a received composite signal containing a number ofcodes in order to separate out one or more individually coded signalsfrom the composite signal.

Good cross-correlation properties cannot always be obtained among agroup of selected codes. Furthermore, multipath in a radio channel canchange the cross-correlation properties of a signal before a signalarrives at a receiver. Therefore, there are some instances where thecross-correlation among signals is good, and other instances when thecross correlation deteriorates. Poor cross correlation may lead toinadequate radio link performance, an increase in bursts of data errors,and loss of the spectral efficiency of the system.

BRIEF SUMMARY OF THE INVENTION

Some embodiments of the present invention provide a method oftransmitting data on a link from a first radio to a second radio acrossa plurality of timeslots in a frame, the method comprising: associatinga first portion of user data with a first portion of the frame;associating a second portion of user data with a second portion of theframe; encoding the first portion of user data with a first spreadingsequence; encoding the second portion of user data with a secondspreading sequence, wherein the first spreading sequence differs fromthe second spreading sequence; transmitting, from the first radio to thesecond radio, the encoded first portion of user data in the firstportion of the frame; and transmitting, from the first radio to thesecond radio, the encoded second portion of user data in the secondportion of the frame.

Some embodiments of the present invention provide a method wherein atimeslot includes the first portion of the frame and the second portionof the frame. Some embodiments of the present invention provide a methodwherein the first portion of the frame includes a first timeslot of theframe and the second portion of the frame includes a second timeslot ofthe frame, wherein the second timeslot is different than the firsttimeslot. Some embodiments of the present invention provide a methodwherein the first timeslot and the second timeslot are adjacenttimeslots. Some embodiments of the present invention provide a methodwherein the first timeslot and the second timeslot are timeslotsseparated by at least one timeslot period.

Some embodiments of the present invention provide a method furthercomprising: encoding a third portion of user data with a third spreadingsequence; encoding a fourth portion of user data with the fourthspreading sequence, wherein the fourth spreading sequence is differentfrom the third spreading sequence; transmitting, from the first radio tothe second radio, the encoded third portion of user data in a firstportion of a second frame, wherein the first portion of the second framecorresponds to the first portion of the first frame; and transmitting,from the first radio to the second radio, the encoded fourth portion ofuser data in a second portion of the second frame, wherein the secondportion of the second frame corresponds to the second portion of thefirst frame. Some embodiments of the present invention provide a methodfurther comprising applying forward error correction over multipletimeslots in a frame.

Some embodiments of the present invention provide a method furthercomprising applying interleaving over multiple timeslots. Someembodiments of the present invention provide a method wherein the firstspreading sequence includes a first scrambling code and wherein thesecond spreading sequence includes a second scrambling code differentfrom the first scrambling code. Some embodiments of the presentinvention provide a method wherein: transmitting, from the first radioto the second radio, the encoded first portion of user data in the firstportion of the frame includes transmitting a first midamble sequence;and transmitting, from the first radio to the second radio, the encodedsecond portion of user data in the second portion of the frame includestransmitting a second midamble sequence different from the firstmidamble sequence.

Some embodiments of the present invention provide a method furthercomprising: determining the first spreading sequence for the firstportion of user data; and determining the second spreading sequence forthe second portion of user data. Some embodiments of the presentinvention provide a method wherein the link includes an uplink, whereinthe first radio includes a mobile radio, and wherein the second radioincludes a base station. Some embodiments of the present inventionprovide a method wherein the link includes a downlink, wherein the firstradio includes a base station, and wherein the second radio includes amobile radio.

Some embodiments of the present invention provide a code diversitytransmitter comprising: logic to accept user data; code mapping anddistribution logic, wherein the code mapping and distribution logic isoperable to parse user data into a first portion of user data and asecond portion of user data; encoding logic operable to encode the firstportion of user data with a first spreading sequence and operable toencode the second portion of user data with a second spreading sequencedifferent from the first spreading sequence; and a transmitter coupledto the encoding logic and operable to transmit encoded user data.

Some embodiments of the present invention provide a code diversitytransmitter further comprising forward error correction (FEC) logicoperable to apply forward error correction to user data, the FEC logiccoupled between the logic to accept user data and the code mapping anddistribution logic. Some embodiments of the present invention provide acode diversity transmitter further comprising logic to applyinterleaving, the interleaving logic coupled between the logic to acceptuser data and the code mapping and distribution logic. Some embodimentsof the present invention provide a code diversity transmitter whereinthe first portion of user data includes a timeslot block of data. Someembodiments of the present invention provide a code diversitytransmitter wherein the first spreading sequence includes a firstscrambling code and the second spreading sequence includes a secondscrambling code different from the first scrambling code.

Other features and aspects of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings which illustrate, by way of example, the featuresin accordance with embodiments of the invention. The summary is notintended to limit the scope of the invention, which is defined solely bythe claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a model of an uplink TDD CDMA encoding, transmission andreception system in accordance with the present invention.

FIG. 2 shows a TDD CDMA timeslot burst in accordance with the presentinvention.

FIG. 3 shows a form of code diversity using frame-based cell ID cyclingin accordance with the present invention.

FIG. 4 shows a code diversity transmission scheme for low latencytransmission in accordance with the present invention.

FIG. 5 shows a form of code diversity using timeslot-based cell IDcycling in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, reference is made to the accompanyingdrawings which illustrate several embodiments of the present invention.It is understood that other embodiments may be utilized and mechanical,compositional, structural, electrical and operational changes may bemade without departing from the spirit and scope of the presentdisclosure. The following detailed description is not to be taken in alimiting sense, and the scope of the embodiments of the presentinvention is defined by the claims of the issued patent.

Some portions of the detailed description which follows are presented interms of procedures, steps, logic blocks, processing, and other symbolicrepresentations of operations on data bits that can be performed oncomputer memory. A procedure, computer executed step, logic block,process etc. are here conceived to be a self-consistent sequence ofsteps or instructions leading to a desired result. The steps are thoseutilizing physical manipulations of physical quantities. Thesequantities can take the form of electrical, magnetic, or radio signalscapable of being stored, transferred, combined, compared, and otherwisemanipulated in a computer system. These signals may be referred to attimes as bits, values, elements, symbols, characters, terms, numbers, orthe like. Each step may be performed by hardware, software, firmware, orcombinations thereof.

Some CDMA systems select a spreading code from a defined a set ofvalues. In some CDMA systems, such as 3GPP UTRA TDD/FDD systems,spreading codes may be constructed from two components: a channelizationcode component and a scrambling code component. For example, in a 3GPPUTRA TDD CDMA system, a spreading code consists of a scrambling code anda channelization code. Generally, a system may use the channelizationcode component for separating multiple users within a timeslot of a celland the scrambling code component for distinguishing between signalsoriginating from within a cell from signals arriving from other cells.

FIG. 1 shows a model of an uplink TDD CDMA encoding, transmission andreception system. User payload data 110 is provided to a spreader 120 aschannel data (ch₁) 115. The spreader 120 also accepts a spreadingsequence 121 (channelization code C_(c1) 122 and scrambling code C_(s1)123). The spreader 120 encodes the user payload data 110 with aspreading sequence 121 by encoding it with a channelization code(C_(c1)) 122 and with a cell-specific scrambling code (C_(s1)) 123.

Users belonging to a common cell may share the same cell-specificscrambling code (C_(s1)) 123. Users belonging to a different cell willhave a different cell-specific scrambling code (e.g., C_(s2)). Theencoded payload data forms an encoded sequence 125 that is provided to atransmitter (xmtr) 130 and is transmitted as a sequence 135 through aradio channel 140. The radio channel 140 is formed between a userequipment transmitter 130 and a base station receiver 150. The receivedsignal is then processed by the base station to separate each user'spayload data.

FIG. 2 shows a timeslot burst signal 200, for example, a timeslot burstsignal from a TDD CDMA user. The encoded sequence 125 (FIG. 1) isdivided into a first payload section 210 and a second payload section220. A timeslot burst signal 200 consists of the first payload section210 preceding a midamble sequence 230, which is followed by the secondpayload section 220. A receiver uses the known midamble sequence 230 todetermine an impulse response of the radio channel 140 (FIG. 1). Theimpulse response assists the receiver 150 in the detection anddemodulation process.

The properties of the spreading sequence 121, which consists of thechannelization codes 122 and scrambling code 123, play an important partin determining the radio link performance. To better understand thisperformance, consider two interference scenarios: inter-cellinterference and intra-cell interference.

Inter-cell interference is interference that originates from one or moreneighboring cells. When substantial energy from other cells is presentat the receiver in addition to the energy from the home cell, thecross-correlation properties of the received waveforms heavily influencethe link performance. Overlapping sets of channelization codes 122 maybe used within two neighboring cells, a home cell and its neighboringcell. When overlapping channelization codes 122 are used in aneighboring cell, the correlation properties of a received waveform areprimarily influenced by: (1) the scrambling sequences applied within thehome cell; (2) the scrambling sequences 121 applied in the neighboringinterfering cell; and (3) the radio propagation channels through whicheach signal has passed.

If the cross-correlation properties are poor between two or more signalsequences arriving at a receiver during the same timeslot, linkperformance will suffer. Due to the fact that the scrambling componentof the overall spreading sequence 121 is cell specific and the fact thatthe set of available channelization codes 122 is limited to a relativelysmall set of values, there is a potential for spreading sequences 121with poor cross-correlation properties to persistently oppose each otherand to thus persistently degrade system performance.

Unlike inter-cell interference, intra-cell interference is interferencethat originates from within a cell. The channelization codes may bedesigned to be orthogonal such that the selected codes have idealcross-correlation properties. Orthogonality is often destroyed beforesignals reach a receiver. Orthogonality may be destroyed by thetime-dispersive nature of a radio channel. Orthogonality between two ormore uplink signals may also be destroyed if the uplink burststransmitted in the same timeslot arrive at a base station at differenttimes.

Forward error correction (FEC) combined with interleaving of radiotransmissions help to overcome short-term signal power fluctuations(fading) in a radio channel. In these schemes, the data is encoded overa time period that spans multiple fading events and an interleaver isused to distribute the effects of resulting bit errors evenly throughputthe received signal. The power of the forward error correcting code isthen able to recover these small gaps or errors in the received data. Ifa signal is not substantially degraded and if forward error correctionand interleaving work properly, the underlying information content maybe delivered error free.

Forward error correction and interleaving may also help to alleviateerror bursts caused by two signal sequences having instantaneously-poorcross-correlation properties. Forward error correction also provides thebenefit of reducing the overall variability observed in link performanceacross users and the benefit of reducing the same variability in thetime domain. Forward error correction may also improve stability ofprocesses that control the quality of signals passing over the radiolink.

A form of time diversity on a frame-by-frame basis may be used toalleviate some of the effects of inter-cell interference oncross-correlation properties. For example, 3GPP systems implement cellparameter ID cycling. In such systems, each cell is assigned twoscrambling codes. Odd numbered frames are encoded with a firstscrambling code and even frames are encoded with a second scramblingcode.

If a system uses a single scrambling code and is operating in anenvironment where the one selected scrambling code results inconsistently poor cross-correlation properties, the cross-correlationproperties are always poor. If a system uses two scrambling codes in thesame environment, the cross-correlation properties may be poor only halfof the time. If a sequence has poor cross-correlation properties withother signals in one frame, the next sequence may have bettercross-correlation properties in the next frame.

FIG. 3 shows a form of code diversity using frame-based cell ID cycling.In this example, sequences in odd frames in a first cell (Cell #1) use afirst spreading sequence having unique scrambling code (C_(s1)).Sequences in odd frames in a second cell (Cell #2) use a secondspreading sequence having unique scrambling code (C_(s2)). Similarly,sequences in even frames in the first cell use a third scrambling code(C_(s3)). Sequences in even frames in the second cell use a fourthscrambling code (C_(s4)). In this example, the codes used in odd frameshave poor cross-correlation properties between the first and secondcells. Fortunately, the codes used in even frames have goodcross-correlation properties. The change in correlation properties isdue to a change in cell-specific scrambling codes (C_(si)).

In this example, additional link performance may be realized if forwarderror correction is applied over a transmission time interval (TTI)equal to or greater than two radio frames (20 ms). The FEC may beapplied to pairs of frames in a cell. The use of interleaving mayfurther improve the link performance.

In addition to the scrambling code changing with the cell parameter ID,the midamble sequence may also be changed. This can bring about similarrandomization of the cross correlation between arriving midamblewaveforms, which may be exploited to compute better channel estimates inthe receiver.

By moving more error correction and retransmission control functionalitydown from a base station controller, such as an RNC, to a base station,such as a Node-B, a wireless communication system can reduce control,transmission and retransmission latencies. For packet data, minimizinglatency of transmissions is a goal in providing a high perceivedthroughput to the end user. High latency appears simply as a slow datalink to the user, whereas low latency creates a perception in the userof being connected via a high-throughput data link.

With the current 3GPP system of frame-based cell ID cycling, the datamust be transmitted over a 20 ms TTI or greater in order to realize thebenefits of code diversity. This immediately introduces latency onto theradio link and means that transmissions using TTI's less than 20 mscannot benefit from frame-based code diversity. Frame-based codediversity is inadequate for low latency (<20 ms) transmissions with thecurrent 3GPP scheme.

Additionally, the current 3GPP cell parameter ID cyclic is targeted atimproving the situation for the inter-cell interference case. Attentionto the intra-cell interference case is lacking.

In some embodiments of the present invention, the TTI is assumed to beno more than 1 radio frame. Each transmission within the TTI is composedof one or more timeslots. In 3.84 Megachips per second (Mcps) 3GPP UTRATDD, 1 radio frame is 10 ms long and includes 15 timeslots of which upto 14 may be assigned to uplink traffic. Within the system, timeslot andchannelization code resources are likely to be allocated on a relativelyfast basis (e.g., on a frame-by-frame basis) by a network entity, suchas the base station or a base station controller.

The number of timeslots allocated to a user and the assignedchannelization codes is likely to vary according to the data trafficneeds of that user. In general, it will be common for a user to beallocated more than one timeslot per radio frame for a user demandinghigh throughput. In some embodiments, a single code will be allocatedper uplink timeslot. In other embodiments, multiple codes are allocatedper uplink timeslot. In some embodiments, a single code will beallocated per downlink timeslot. In other embodiments, multiple codesare allocated per downlink timeslot.

In some embodiments, the code or codes used for transmission are variedfor each user within a radio frame. Thus, for transmissions spanningmultiple code variation periods within the TTI, and for which forwarderror correction is applied, the benefits of code diversity may berealized and system capacity and performance may be increased.

In some embodiments, a spreading sequence may be changed from timeslotto timeslot by changing the spreading sequence. In some embodiments, thespreading sequence is changed from timeslot to timeslot by changing ascrambling code from timeslot to timeslot. In other embodiments, aspreading sequence may be changed from half-timeslot to half-timeslot.That is, the first half of the payload (210 in FIG. 2) is encoded with afirst spreading sequence and the second half of the payload (220 in FIG.2) is encoded with a second spreading sequence. If the cell is allocatedonly two scrambling codes and is encoding on a half-timeslot bases,every timeslot will be encoded with the same pair of scrambling codes.If the cell is allocated only four scrambling codes and is encoding on ahalf-timeslot bases, every other timeslot will be encoded with the samepair of scrambling codes. If the cell is allocated two scrambling codesand is encoding on a timeslot-by-timeslot bases, every other timeslotwill be encoded with the same of scrambling code.

FIG. 4 shows a code diversity transmission scheme for low latencytransmission. FIG. 4 may apply to either uplink or downlink signals. In410, user data is provided to the encoding system. Some embodimentsinclude a FEC unit 420, an interleaving unit 430, and a codemapping/distribution unit 440. Other embodiments do not include the FEC420 and/or the interleaving unit 430. In some embodiments, the user datais applied to an FEC unit 420. The output of the FEC 420 is provided tothe interleaving unit 430. The input of the code mapping/distributionunit 440 may be user data from 410 or may be user data applied througheither or both 420 and 430.

In some embodiments, the user data is processed with either or both aFEC unit 420 and an interleaving unit 430 as described above. The userdata, either preprocessed or not preprocessed is provided to a codemapping/distribution unit 440. The code mapping/distribution unit 440parses the user data into a sequence of symbols, where a symbolrepresents one or more bits. If timeslot-by-timeslot cyclic encoding isperformed, the code mapping/distribution unit 440 parses the user datainto timeslot blocks of data.

FIG. 4 shows a code mapping/distribution unit 440 parsing the user datainto three paths. The first path of user data is encoded with codesequence 1. The second path of user data is encoded with code sequence2. The N-th path of user data is encoded with code sequence N. Codesequence 1 may represent a unique scrambling code. Alternatively, codesequence 1 may represent a unique spreading sequence. In this example,the three codes (code sequences 1, 2 and N) are different. Threetimeslots full of uplink traffic in one frame are encoded with threedifferent codes. In a frame repeat pattern of 1, the same three codesmay be used for the next three uplink timeslots in the next frame. In aframe repeat pattern of 2, a different three codes may be used for thenext three uplink timeslots in the second frame, and then the originalthree codes may be used again for the next three uplink timeslots in thethird frame.

In some embodiments, each uplink timeslot in a frame is allocated aspreading sequence. Some but not all of the spreading sequences used ina frame may be the same. In some embodiments, each uplink timeslot in aframe is allocated a different spreading sequence. In these embodiments,none of the spreading sequences used in a frame are the same.

In addition to cycling the scrambling sequences or spreading codes, a UEmay also cycle or similarly vary midamble sequences in uplink and/orbursts.

In some embodiments, the code sequence is varied for each section ofpayload data. In other embodiments, the code sequence is varied for eachpayload data.

A 3GPP UTRA TDD receiver is typically a de-correlating receiver. Thede-correlating receivers attempt to undo the effects of the radiochannel and the code sequences used. The signature sequence is theconvolution of the transmission sequence with the radio channel impulseresponse. This task is computationally intensive and as such, is usuallyonly performed once per timeslot or as required such as when the radiochannel or codes used have changed. Thus, the high-complexity part ofthe receiver may be run at least at the rate of change of the codesequences being transmitted.

The variation in the codes used each timeslot may be the same for eachuser, or may differ between users. That is to say that the codevariation may occur on a cell-by-cell basis, a user-by-user basis orboth.

Additionally, either the channelization code or the scrambling codecomponent of the overall spreading sequence may be varied, or both maybe varied. A further possibility is that an extra variable codecomponent is applied on top of the existing codes. By varying thesequences within a short TTI (e.g., within 10 ms), code diversity isachieved while maintaining low latency transmission.

FIG. 5 shows a form of code diversity using timeslot-based cell IDcycling. In the first example, a code repeat pattern of every frameused. A frame is shown to have four uplink timeslots (TS1 to TS4). Thecode sequence C_(s1) is used on user data placed in the first timeslot(TS1). The code sequence C_(s2) is used on user data placed in thesecond timeslot (TS2). The code sequence C_(s3) is used on user dataplaced in the third timeslot (TS1). The code sequence C_(s4) is used onuser data placed in the fourth timeslot (TS2). Therefore, this firstframe of uplink timeslots uses code sequences C_(s1), C_(s2), C_(s3) andC_(s4). Since the repeat pattern is every frame, the next frame alsouses code sequences C_(s1), C_(s2), C_(s3) and C_(s4).

In the second example, a code repeat pattern of every other frame used.A first frame is shown to have four uplink timeslots (TS1 to TS4). Thecode sequence C_(s1) is used on user data placed in the first timeslot(TS1). The code sequence C_(s2) is used on user data placed in thesecond timeslot (TS2). The code sequence C_(s3) is used on user dataplaced in the third timeslot (TS1). The code sequence C_(s4) is used onuser data placed in the fourth timeslot (TS2). Therefore, this firstframe of uplink timeslots uses code sequences C_(s1), C_(s2), C_(s3) andC_(s4). Since the repeat pattern is every other frame, the second frameuses code sequences C_(s5), C_(s6), C_(s7) and C_(s8). Code sequencesC_(s1), C_(s2), C_(s3) and C_(s4) are uses again as shown in the thirdframe.

In some embodiments of the present invention, a method varies thescrambling code assigned to a cell on a per timeslot basis. In order toenable correct decoding, the variation pattern may be known to both theuser and to the base station and may be synchronized between thetransmitter and the receiver. In some embodiments of the presentinvention, the code variation pattern is pre-determined and known apriori by both transmitter and receiver. In some embodiments of thepresent invention, the code variation pattern is signaled by the networkto the user terminal at the start of or sometime during the connection.In some embodiments of the present invention, the code variation patternis derived by means of an algorithm known to both the transmitter andthe receiver and a seed-value or other parameter is signaled at thestart of or sometime during the connection. In some embodiments of thepresent invention, the code variation pattern is a function of a systemparameter known to both the transmitter and receiver. For example, thesystem parameter may be the system frame number. In some embodiments ofthe present invention, the code variation pattern itself may also bechanged at times determined or signaled by the network, or atpredetermined times known to both the receiver and transmitter.

In some embodiments of the present invention, the spreading codes usedmay come from the existing set of defined scrambling and channelizationsequences or may be completely new sequences. Alternatively, a new setof sequences could be derived using arithmetic or algorithmic meansusing the existing sequences as functional inputs.

In some embodiments of the present invention, the midamble sequence usedfor transmission may also be varied in a similar manner to the codesapplied to the payload sections of the burst(s).

Some embodiments of the present invention provide a method oftransmission in a TDD CDMA system capable of realizing code diversitybenefit for low latency transmissions comprising a transmitter capableof changing the code sequences used for transmission one or more timesduring transmission of one or more interleaved forward error correctiondata units. The code sequence may be changed multiple times within aradio frame. Some embodiments of the present invention provide areceiver synchronized to the varying code pattern applied in thetransmitter, performing de-interleaving and error correction decoding ofthe received data unit(s).

Some embodiments of the present invention provide a method in which thetransmission code is varied by means of changing the scrambling code oneor more times during the transmission of a forward error correction dataunit in which the scrambling codes used are: (1) from the existing setof defined scrambling codes for 3GPP TDD CDMA; (2) derived byarithmetical or algorithmic means from the existing set of definedscrambling codes for 3GPP TDD CDMA; and/or (3) any new set of scramblingcodes. Some embodiments of the present invention provide a method inwhich the transmission code is varied by means of changing thechannelization code one or more times during the transmission of aforward error correction data unit in which the channelization codesused are: (1) members of the set of defined channelization codes for3GPP TDD CDMA; and/or (2) any new set of channelization codes. Someembodiments of the present invention provide a method in which thetransmission code is varied by means of changing both the scramblingcode and the channelization code one or more times during thetransmission of a forward error correction data unit. Some embodimentsof the present invention provide a method in which the transmission codeis varied by means of applying an extra code on top of the existingchannelization and scrambling codes during the transmission of a forwarderror correction data unit.

Some embodiments of the present invention provide a method in which thecode variation pattern is implicitly known a priori to both transmitterand receiver. Some embodiments of the present invention provide a methodwhich the code variation pattern is signaled explicitly to thetransmitter by network or base station. Some embodiments of the presentinvention provide a method in which the code variation pattern isderived via algorithmic or arithmetical means based upon parameters:known a priori to both transmitter and receiver; signaled to thetransmitter by a network or base station; and/or derived from anothersystem parameters known to both transmitter and receiver or signaled tothe transmitter by a network. Some embodiments of the present inventionprovide a method in which the transmission code is varied on aper-timeslot basis. Some embodiments of the present invention provide amethod in which the transmission code is varied on a sub-timeslot basis(e.g.: per data payload, per ½ payload, or per symbol). Some embodimentsof the present invention provide a method in which the transmission codeis varied on a per-timeslot or sub-timeslot basis by means of changingthe scrambling code and/or channelization code, and or anadditionally-applied code.

Some embodiments of the present invention provide a method as describedby any of the above features as applied to a 3GPP TDD CDMA uplinksystem, including legacy uplink channels and/or enhanced uplinkchannels. Some embodiments of the present invention provide a method asdescribed by any of the above features as applied to a 3GPP TDD CDMAdownlink system, including legacy downlink channels, HSDPA and futuredownlink channels. Some embodiments of the present invention provide amethod as per any of the above in which the midamble sequence used forburst transmission is also varied as a function of the variation appliedto the scrambling/channelization/additional codes.

While the invention has been described in terms of particularembodiments and illustrative figures, those of ordinary skill in the artwill recognize that the invention is not limited to the embodiments orfigures described. The figures provided are merely representational andmay not be drawn to scale. Certain proportions thereof may beexaggerated, while others may be minimized. The figures are intended toillustrate various implementations of the invention that can beunderstood and appropriately carried out by those of ordinary skill inthe art. Therefore, it should be understood that the invention can bepracticed with modification and alteration within the spirit and scopeof the appended claims. The description is not intended to be exhaustiveor to limit the invention to the precise form disclosed. It should beunderstood that the invention can be practiced with modification andalteration and that the invention be limited only by the claims and theequivalents thereof.

1. A method of transmitting data on a link from a first radio to asecond radio across a plurality of timeslots in a frame, the methodcomprising: encoding user data using a forward error correcting code togenerate an encoded bit sequence, wherein the user data is data for asingle user; generating a first spread portion of the encoded bitsequence with a first spreading sequence associated with a first portionof the frame, the first spreading sequence based on a firstchannelization code and a first scrambling code; generating at least asecond spread portion of the encoded bit sequence with a secondspreading sequence associated with a second portion of the frame, thesecond spreading sequence based on a second channelization code and asecond scrambling code, wherein the first channelization code differsfrom the second channelization code according to a predetermined codevariation pattern; and transmitting, from the first radio to the secondradio, the frame including the first spread portion and the at leastsecond spread portion of the encoded bit sequence.
 2. The method ofclaim 1, wherein a timeslot includes the first portion of the frame andthe second portion of the frame.
 3. The method of claim 1, wherein thefirst portion of the frame includes a first timeslot of the frame andthe second portion of the frame includes a second timeslot of the frame,wherein the second timeslot is different than the first timeslot.
 4. Themethod of claim 3, wherein the first timeslot and the second timeslotare adjacent timeslots.
 5. The method of claim 3, wherein the firsttimeslot and the second timeslot are timeslots separated by at least onetimeslot period.
 6. The method of claim 1, further comprising:generating a third spread portion of the encoded bit sequence with athird spreading sequence associated with a first portion of a secondframe, the third spreading sequence based on a third channelization codeand a third scrambling code; generating a fourth spread portion of theencoded bit sequence with the fourth spreading sequence associated witha second portion of the second frame, wherein the fourth spreadingsequence is based on a fourth channelization code and a fourthscrambling code, wherein the third channelization code differs from thefourth channelization code; and transmitting, from the first radio tothe second radio, the second frame including the third spread portionand the fourth spread portion of the encoded bit sequence.
 7. The methodof claim 6, wherein the third spreading sequence is the first spreadingsequence, and the fourth spreading sequence corresponds to the secondspreading sequence according to the predetermined code variationpattern.
 8. The method of claim 6, wherein the third spreading sequenceand the fourth spreading sequence differ from the first spreadingsequence and the second spreading sequence according to thepredetermined code variation pattern.
 9. The method of claim 1, whereinencoding the user data using the forward error correction code is over atransmission time interval of a single frame.
 10. The method of claim 1,wherein encoding the user data using the forward error correction codeis over multiple timeslots in a frame.
 11. The method of either claim 9or 10, further comprising applying interleaving over multiple timeslots.12. The method of claim 1, wherein the first scrambling code isdifferent from the second scrambling code.
 13. The method of claim 1,wherein transmitting, from the first radio to the second radio, theframe including the first spread portion and the second spread portionincludes transmitting a first midamble sequence along with the firstspread portion and a second midamble sequence along with the secondspread portion, wherein the first midamble sequence differs from thesecond midamble sequence.
 14. The method of claim 1, further comprising:determining the first spreading sequence for the first portion of theencoded bit sequence; and determining the second spreading sequence forthe second portion of the encoded bit sequence.
 15. The method of claim1, wherein the link includes an uplink, wherein the first radio includesa mobile radio, and wherein the second radio includes a base station.16. The method of claim 1, wherein the link includes a downlink, whereinthe first radio includes a base station, and wherein the second radioincludes a mobile radio.
 17. The method of claim 1, wherein the firstscrambling code corresponds to the second scrambling code.
 18. A codediversity transmitter comprising: logic to accept user data; forwarderror correction (FEC) logic operable for encoding user data of a singleuser using a forward error correcting code to generate an encoded bitsequence, the FEC logic coupled between the logic to accept user dataand the code mapping and distribution logic, wherein the user data isdata for a single user; code mapping and distribution logic, wherein thecode mapping and distribution logic is operable to parse the encoded bitsequence into a first portion and at least a second portion; spreadinglogic operable for generating the first spread portion of the encodedbit sequence with a first spreading sequence, the first spreadingsequence based on a first channelization code and a first scramblingcode, and the spreading logic further operable for spreading the atleast second spread portion of the encoded bit sequence with a secondspreading sequence, the second spreading sequence based on a secondchannelization code and a second scrambling code, wherein the firstchannelization code differs from the second channelization codeaccording to a predetermined code variation pattern; and a transmittercoupled to the encoding logic and operable for transmitting the firstspread portion and the at least second spread portion of the encoded bitsequence.
 19. The code diversity transmitter of claim 18, furthercomprising interleaving logic for applying interleaving, theinterleaving logic coupled between the logic to accept user data and thecode mapping and distribution logic.
 20. The code diversity transmitterof claim 18, wherein the first portion of the encoded bit sequenceincludes a timeslot block of data.
 21. The code diversity transmitter ofclaim 18, wherein the first scrambling code differs from the secondscrambling code.
 22. The code diversity transmitter of claim 18, whereinthe first scrambling code corresponds to the second scrambling code.